1. Field of the Invention
The present invention relates to a surge counter which is provided on various lines, such as a surge counter for power supply lines and communication lines to count the number of times invading surges invade into these lines.
2. Description of the Related Art
If surges invade power supply lines for communication equipment such as telephone sets, facsimiles, telephone switching boards, modems, and the like, the communication equipment's electronic circuits are damaged by a fire. Therefore, conventionally, surge absorbers are provided on input lines of the power supply line, communication line and the like for communication equipment which is installed in a region where the surges tend to generate.
In order to protect the communication equipment from surges securely by means of the surge absorber, the specifications of the surge absorbers must be determined based on the results of statistical investigations of the generating times of the surges around the area where the communication equipment is to be installed.
Conventionally, for example, a surge counter for recording the number of times of invading surges has been disclosed in Unexamined Published Japanese Patent Application No.59-211984. The aforementioned surge counter comprises: a surge detecting element which is connected to the surge invading line and which is formed by connecting a gap type glass sealed discharge tube and a nonlinear resistor in series; a light receiving element for detecting a light emission from the discharge tube; and a counter circuit for counting the signals detected from the light receiving element. In this counter, since the surge input circuit and the surge detecting circuit are independent, there is no possibility that the surge will be detected by the detecting circuit, and besides, the advantage for the design of the detecting circuit to be done easily exists.
Moreover, in the foregoing conventional surge counter, a surge current withstanding capability of the surge current detecting element is selected by relating it to another surge current withstanding capability which is provided by the glass sealed discharge tube and the nonlinear resistor in series therewith. Hence, in case a surge current exceeds the surge current withstanding capability of the glass sealed discharge tube and the nonlinear resistor, such surge then invades into the surge current detecting element, and there is a fear that the glass sealed discharge tube or nonlinear resistor may be destroyed.